A cataract is a condition where the lens of the eye becomes opaque ultimately leading to impaired vision. Cataracts are the main cause of blindness worldwide. Treatment consists of a surgical procedure wherein the cataract is extracted and replaced with an intraocular lens.
A central circular capsulorhexis of appropriate size and edge integrity is the key to successful cataract surgery. This is where a continuous circular incision is made in the anterior capsule that then allows for safe phacoemusification surgery and determines centration and stability of the capsular-fixated intraocular lens.
Although cataract extraction aims to remove the content of the capsular bag (the outer layer of the crystalline lens), invariably some lens epithelial cells are left behind, on the inner aspect of the lens capsule. Human capsular bags contain a large population of viable cells for many years after cataract surgery. In this environment an “after-cataract” may be formed, caused by the proliferation of lenticular epithelial cells, fibroblasts, macrophages and even iris-derived pigment cells on the lens capsule.
In order to counteract this problem, technologies have been developed for removing the lens epithelial cells, however these techniques cannot remove other cell types that can invade the capsule from the ocular aqueous humour circulation or iris.
As a result, these various cell populations participate in a fibrotic process whereby the anterior capsule opening after capsulorhexis gradually constricts to some extent. This contraction (or phimosis) of the anterior capsule opening can occur excessively in children, young adults and in certain pathological states—including diabetes, retinitis pigmentosa, pseuodexfoliation of the lens capsule, myotonic dystrophy, glaucoma and uveitis.
At present, in routine surgery, the aim is to create a capsulorhexis of appropriate size, typically 5.5 mm for an intraocular lens with an optic diameter of 6 mm. It is thought that this symmetrical overlap of anterior capsule over the periphery of the intraocular lens “shrink-wraps” the intraocular lens.
As phimosis occurs, the encroaching anterior capsule can be incised using a Yag laser or by open operation. This can relieve the capsule contraction but can also result in complications such as retinal detachment, macular oedema, lens dislocation and presentation of vitreous into the anterior eye. If the capsulorhexis is made larger than this (to “overcompensate” for future phimosis), the anterior and posterior leaves of the capsule can fuse in an asymmetric fashion, resulting in “peapoding” where the intraocular lens is displaced away from the visual axis, resulting in reduced vision.
Removal of anterior subcapsular epithelial cells by aspiration helps maintain the size of the capsulorhexis opening (6 month follow up) but it is uncertain as to whether this prevents capsule contraction syndrome in the longer term
In certain cases, the fibrosis is so extensive that the anterior lens surface is covered over, resulting in marked reduction in vision. As the lens capsule is attached to the inner wall of the eye (over the ciliary body) by delicate zonular fibres, the fibrotic process can result in the zonular support being pulled off the ciliary body and the whole of the capsular bag containing the intraocular lens can dislocate into the vitreous body.
The capsular tension ring (CTR) was originally introduced to reinforce the zonule in eyes with zonular dehiscence and to prevent capsular phimosis in eyes at risk for postoperative capsular shrinkage. Yet despite insertion of CTR's capsule phimosis can still occur.
Accordingly, the present invention seeks to provide a device and method for maintaining the structural integrity of anterior capsule opening formed as a result of a capsulorhexis and reduce the risk of phimosis occurring after cataract surgery.